DIELECTRIC-DISPERSION OF THE DIPOLAR GLASS K0.989LI0.011TAO3

Dielectric dispersion spectra measured on K0.989Li0.011TaO3 at frequencies 10(-3) less-than-or-equal-to f less-than-or-equal-to 10(7) Hz and temperatures 5 less-than-or-equal-to T less-than-or-equal-to 100 K are analyzed in terms of Lacroix-Bene type distributions of relaxation times, G(tau) is-proportional-to (tau - tau(o))-beta. Tau(o) is related to the local hopping diffusion of isolated off-center Li+ dipoles. It varies as exp(DELTAE/k(B)T) with DELTAE/k(B) = 910 K at T > 40 K and crosses over into the quantum tunneling limit, tau(min) approximately 10(2) s as T --> 0. The exponent beta decreases with decreasing T, beta approximately 0.05 as T --> 30 K, in accordance with the observed asymmetric low-frequency broadening of epsilon'' vs log f. Upon approaching the static freezing temperature, T(g) = 33.7 K, power law divergence of tau(max) with an exponent znu = 15.1 is observed.